RFR (xxs) JDK-8012525 gc/metaspace/G1AddMetaspaceDependency.java Test fails a safepoint timeout assertion or hangs.

[Mikael Gerdin]

On 10/02/2013 12:52 PM, Bengt Rutisson wrote:
>
> Hi Mikael,
>
> Looks good.

Thanks, Bengt.
/Mikael

>
> Bengt
>
>
> On 10/1/13 11:44 AM, Mikael Gerdin wrote:
>> Hi
>>
>> Please review this small test fix to work around a problem where the
>> test accidentally provokes a very slow execution path in the VM.
>> This slow path can cause very long GC pauses or delayed safepoints.
>>
>> Summary of the bug:
>> The byte array allocation causes a big MemRegion to be stored as the
>> thread's deferred_card_mark. This can cause two separate slow code paths:
>>
>> * A slow GC pause because CollectedHeap::ensure_parsability flushes
>> the cards through the VM barrier code and dirtying a large region is
>> expensive with the small G1UpdateBufferSize.
>> * A thread_in_java being slow in reaching safepoint because it's
>> flushing the cards in OptoRuntime::new_array_C at the call to
>> new_store_pre_barrier, this ends up in the same code as
>> ensure_parsability and can therefore be slow.
>>
>> I've ran the test with the large allocation removed and it still
>> successfully reproduces the bug it was written to provoke on an
>> unfixed build, so my suggestion is to simply remove the byte array
>> allocation.
>>
>> The bug is unfortunately not externally visible.
>>
>> Webrev: http://cr.openjdk.java.net/~mgerdin/8012525/webrev
>>
>> /Mikael
>